1. Field of the Invention
The present invention relates to an image display device, and more particularly, to an image display device for displaying a two-dimensional plane image (referred to as ‘2D image’, hereinafter) and a three-dimensional stereoscopic image (referred to as ‘3D image’, hereinafter).
2. Discussion of the Related Art
An image display device displays a 3D image using a stereoscopic technique or an autostereoscopic technique. The stereoscopic technique, which uses a parallax image of left and right eyes of a user with a high stereoscopic effect, includes a glass method and a non-glass method which have been put to practical use. In the glass method, a left and right parallax image is displayed on a direct view-based display device or a projector by changing a polarization direction of the left and right parallax image or in a time division method, and a stereoscopic image is implemented by using polarization glasses or liquid crystal shutter glasses. In the non-glass method, generally, an optical plate such as a parallax barrier or the like for separating an optical axis of the left and right parallax image is installed in front of or behind the display screen.
As shown in FIG. 1, the glass method may include a patterned retarder 5 for converting polarization characteristics of light incident on the polarization glasses 6 from the display panel 3. In the glass method, a left eye image (L) and a right eye image (R) are alternately displayed on the display panel 3, and the polarization characteristics of light incident on the polarization glasses 6 are converted by the patterned retarder 5. Through this operation, the glass method implements a 3D image by spatially dividing the left eye image (L) and the right eye image (R). In FIG. 1, reference numeral 1 denotes a backlight that irradiates light to the display panel 3, and 2 and 4 denote polarizers attached on upper and lower surfaces of the display panel 3 to select a linear polarization, respectively.
With such glass methods, visibility of the 3D image is degraded due to crosstalk generated at the position of an up/down viewing angle, thereby narrowing the up/down viewing angle. The crosstalk is generated because the left eye image (L) passes through the right eye patterned retarder region as well as the left eye patterned retarder region and the right eye image (R) passes through the left eye patterned retarder region as well as the right eye patterned retarder region at the up/down viewing angle position, as shown in the shaded portions of the polarization glasses 6 in FIG. 1. In the polarization glasses 6 in FIG. 1, the shaded portion shows the right image and the non-shaded portion shows the left image. Thus, a Japanese Laid Open Publication No. 2002-185983 discloses a method for obtaining a wider up/down viewing angle by forming black stripes (BS) at the patterned retarder regions corresponding to black matrixes (BM) of the display panel to improve the visibility of the 3D image, as shown in FIG. 2. In FIG. 2, when observed at a certain distance (D), a viewing angle (α), at which crosstalk is theoretically not generated, depends on the size of black matrixes (BM) of the display panel, the size of the black stripes (BS) of the patterned retarder, and the size of the spacer (S) between the display panel and the patterned retarder. The viewing angle (α) widens as the sizes of the black matrixes and the black stripes increases and as the spacer (S) between the display panel and the patterned retarder decreases. However, the related art has the following problems.
First, the black stripes of the patterned retarder aimed for improving the visibility of the 3D image through enhancement of the viewing angle interact with the black matrixes of the display panel, thereby generating moiré. Accordingly, when a 2D image is displayed, the visibility of the 2D image is degraded. FIG. 3 shows the results obtained by observing a display device sample with a size of 47 inches at a location 4 meters away from the display device with black stripes. When a 2D image is displayed, moirés of 90 mm, 150 mm, and 355 mm are generated for observation positions A, B, and C, respectively.
Second, the black stripes aimed for improving the visibility of the 3D image through enhancement of the viewing angle creates a side effect that the luminance of the 2D image is degraded. As shown in FIG. 4(b), this is because certain portions of pixels of the display panel are covered by the black stripe patterns. Accordingly, when the 2D image is displayed, the amount of transmitted light decreases by about 30% compared with the case where black strips are not formed, as shown in FIG. 4(a).